Antenna housing



Nov. 11, 1952 E. B. MOMILLAN ETAL ANTENNA HOUSING Filed May 2, 1945 FIG.|

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N R mum mu m VWW m Mn BM D m 0 M ww RB ATTORNEY Patented Nov. 11, 1952 ANTENNA HOUSING Edward B. McMillan, Greenwood, and Raymond M. Redheffer, Cambridge, Mass., assignors, by mesne assignments, to the United States of America as represented by the Secretary of War Application May 2, 1945, Serial No. 591,585

1 Claim. 1

This invention relates in general to antenna housings and more particularly to antenna housings having laminated construction.

I In radio communication systems employing carrier frequencies in the ultra high frequency and microwave hands, it is practicabl to use antenna housings because of the reduced size of the antenna apparatus. Such housing plays an important part in antenna assemblies because it protects delicate antenna assemblies against inclement weather, blows from solid objects, and strong wind pressures encountered in airborne installations.

A housing, consisting of on layer of plywood, plastic, or other material which is transparent to radio energy, will aflord the advantages mentioned above. However, the electromagnetic waves radiated from the antenna within the housing will be reflected at least in part from any surface which separates media of different dielectric constants. This means that, in general, there will be reflection from the housing, since any material of which it may be made will have a. dielectric constant appreciably different from that of the surrounding air. Such reflections reduce the amount of electromagnetic energy eventually transmitted through the wall; moreover, these reflections distort the predetermined energy distribution pattern of the antenna.

In many high frequency radio communication systems, it is desired to enclose in a housing a highly directional rotatable antenna. The magnitude and phase of the energy reflected by the housing wall may vary with the position of the antenna because of non-uniform transparency of the housing. A portion of the reflected energy may be absorbed by the antenna and communicated back to the transmitter so that a nonuniform impedance is presented to the radio frequency generator. This may result in a condition of frequency instability.

Therefore, it is one object of the present invention to provide an antenna housing which minimizes undesirable reflections.

Another object is to provide an antenna housing which will have desired transmission characteristics and will also protect antenna assemblies from wind, weather, and accidental blows, and which is lightweight, yet strong.

These and further objects of this invention will be evident to those skilled in the art upon reference to the following specification, claim, and drawings, in which:

Fig. 1 shows several possible antenna installations to which a housing of the type disclosed herein is especially adaptable; and

Fig. 2 shows a cross-sectional view of thewa-ll construction of such a housing.

Briefly, the invention consists of laminating two dissimilar materials in a sandwich fashion,

yielding a three-ply sheet with a low density, low dielectric core surrounded by thin skins of high mechanical strength. The materials comshown. An airplane 5, carrying an ultra high frequency radio communication system, may have the antenna for the system mounted in th nose of the plane, in which case the housing 6 will bea continuation of the outer skin of the-plane. An antenna may also be mounted in a turret-like housing I on the upper side of the plane, or

alternatively, as at 8, on the under side. These turrets may be retractable if it is so desired. It is to be emphasized that these three alternatives do not exhaust the possible uses of antenna housings but are presented only as examples.

In Fig. 2, a section of housing wall is shown.

It consists of two skins I 0 and II of the same thickness d and di-electric constants a, and a core l2 having a dielectric constant B, and a thickness at.

Double wall housings are well known in the art, having been developed to reduce the objectionable reflections described hereinabove. These double wall housings generally consist of two skins separated by spacers placed at intervals around the housing. A major difliculty with this type of structure is the non-uniform wall thickness, this variable wall thickness afiecting the transmission of extremely high frequencies or microwaves through a housing. The wall tolerance is a function of wavelength; the shorter the wavelength, the closer the tolerance. Also, the wall thickness tolerance is a function of skin thickness, tolerance and skin thickness varying inversely. It can be seen that the application of external forces to such a housing may flex the outer skin, altering th skin spacing with adverse effect. Alternatively, if the skin is made thick enough to be rigid, the tolerances allowable are too great to allow ease of manufacture.

The sandwich type housing has the advantages of the simple double wal1 type without its disadvantages. Th core can be manufactured to accurate thicknesses, and very thin, mechanically strong skins can be bonded thereto. The use of a sandwich composition for mechanical strength is not novel. However, heretofore such construction has not been made according to optiwhere mum electrical properties, X=thickness of said core A principal factor in minimizing reflections is \=free space wavelength of electromagnetic the core thickness. It has been found, that for energy a normally incident electromagnetic wave, it is N=any integer possible to obtain the optimum core thickness in a=dielectric constant of said skins terms of the other variables of the sandwich, fi=dielectric constant of said core, and using the expression: d=thickness of said skins wher i e 20 whereby energy reflections from saidv skins and Xzoptimum thickness of core I2 said core will combine in a subtractive manner \=freespace wavelength of electromagnetic when radiant energy i p opa ted in a direction energy normal to said housing wall, thus to provide sat- Nlany integer isfactory transmission characteristics through ;-=dielectr-1c constant of skins l0 and l l 25 Said housing- :dielectric constant of core I2 I EDWARD B. McMILLAN. d=thickness of skins l0 and H v RAYMOND M. REDHEFFER.

- A'housing constructed according to this rela- REFERENCES CITED tion will exhibit electrical characteristics marked- 1y improved over previous types of housings, and U0 The following references are of record in, the

advantages of mechanical strength and ease of me of thls patent:

manufacture as elaborated hereinbefore. It will, UNITED STATES PATENTS of. course, be understood that slight departures Number Name Date from optimum values may be tolerated without 1 557 049 Hammond Oct 13 1925 substantial loss of the values of the invention. 2202:380 Hellman i, 1940 fwhat 1s clalmed 2,223,224 Newhouse Nov. 26 1940 7 An antenna housing having a wall construc- 2 304 540 Cassen Dec 8 1942 tion c'omprising two skins of predetermined thick-'- 2376653 Boyer 1945 ness spaced apart by a core also of predeter- A0 2405992 Bruce mined thickness, said skins being substantially 2407911 Tonks "s compOSition and thickness, said Skins 24 and said cor being of material transparent to 2415352 Iams b radiant electromagnetic energy, said wall being 221171052 Bemofff M 1947- proportioned substantially according to the following relationship: 45 

